This invention relates to integrated optic devices and more particularly to those devices which include an optical waveguide having a bend.
A fundamental consideration in the design of integrated optical circuits is the packing density of components on a substrate. This is limited principally by the angles through which waveguides may be turned in order to access each component. In presently known semiconductor optical circuits, much of the substrate area is taken up with waveguides fanning into and out of devices, or clusters of devices, at low angles, typically about one degree.
A number of techniques have been proposed to enable the bend angle of optical waveguides to be increased without unacceptable losses being sustained in bending light around corners. One proposed solution is to "chamfer" the bend so that its outer region is removed. This method is illustrated in FIG. 1 where the waveguide 1 includes a bend at 2, the outer part of which is chamfered, as shown at 3. The intensity of light entering from the left of the waveguide, in the direction shown by the arrow, is represented by the weight of shading of different regions of the waveguide 1 and the surrounding structure. Although chamfering gives satisfactory results for low angle bends of, say, less than one degree in the case of weakly guiding structures, it does not offer good enough performance to make it a viable technique for higher angle bends.